Coordination of a Hemilabile N,N,S Donor Ligand in the Redox System [CuL 2 ] +/2+ , L = 2‐Pyridyl‐ N ‐(2′‐alkylthiophenyl)methyleneimine

The new copper(I) complexes [Cu(L 1 ) 2 ](BF 4 ), L 1 = 2‐pyridyl‐ N ‐(2′‐methylthiophenyl)methyleneimine, and [Cu(L 2 ) 2 ](ClO 4 ), L 2 = 2‐pyridyl‐ N ‐(2′‐benzylthiophenyl)methyleneimine, have been prepared and structurally characterized. In contrast to the known [Cu(L 1 ) 2 ](ClO 4 ) 2 , which exhibits partial thioether S binding to effect five‐coordinate Cu 2+ , the copper(I) compounds reported here contain four‐coordinate metal ions with exclusively N‐donor binding. Cyclic voltammetry reveals a fully reversible oxidation of the Cu I species, which suggests a small barrier for reorganization. The reduction at negative potentials is irreversible for compounds [Cu(L) 2 ](X) and for the structurally characterized new compound [Cu(L 1 )(PPh 3 ) 2 ](ClO 4 ). UV/Vis spectroelectrochemistry shows the typical low‐energy absorption bands of copper(I) (MLCT transition) and copper(II) (ligand‐field transition) in the visible region; the Cu II form develops an intense band at 350 nm attributed to a S‐to‐Cu ligand‐to‐metal charge transfer (LMCT).